The human KCNQ1 voltage-gated potassium channel is modulated by interactions with an accessory subunit, KCNE1, a process that is essential for healthy cardiac and auditory function. Mutations in KCNQ1 and KCNE1 result in congenital long QT syndrome (LQTS) and some forms of deafness. KCNE1 acts both to slow down voltages-stimulated channel activation and also dramatically enhances the conductance of the open state. Other KCNE family members exert radically different changes in KCNQ1 channel function. In the upcoming phase of this project the aims are: Aim 1. Use NMR to determine the 3-D structure of KCNE1 under conditions in which it is solubilized in actual lipid bilayers. This aim will test whether the structure of KCNE1 we recently determined in classical micelles represents the bona fide structure of the protein in lipid bilayers, or whether elements of the determined structure that were crucial in formulating our working model for KCNE1 function were, in fact, artifacts of working in micelles. Aim 2. Using mutagenesis of both KCNE1 and KCNQ1, biochemical measurements, and electrophysiological recordings of KCNQ1 channel properties, critically evaluate and refine the current working model for how KCNE1 slows down KCNQ1 channel opening and enhances open state conductance. Aim 3. Determine the 3-D structure of KCNE3 in bilayers and formulate a working model for how KCNE3 rapidly activates Q1 channel function. Aim 4. Carry out structure-function and biochemical testing/refinement of the new model for how KCNE3 rapidly activates KCNQ1 channel function. Aim 5. Determine the structure of KCNE4 in bilayers and formulate a working model for how KCNE4 inhibits KCNQ1 channel function.